EP0500979B1 - Dispositif de détection de gaz avec un capteur électrochimique et une barrière de diffusion variable - Google Patents

Dispositif de détection de gaz avec un capteur électrochimique et une barrière de diffusion variable Download PDF

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Publication number
EP0500979B1
EP0500979B1 EP91102870A EP91102870A EP0500979B1 EP 0500979 B1 EP0500979 B1 EP 0500979B1 EP 91102870 A EP91102870 A EP 91102870A EP 91102870 A EP91102870 A EP 91102870A EP 0500979 B1 EP0500979 B1 EP 0500979B1
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EP
European Patent Office
Prior art keywords
diffusion
valve
sensor
opening
openings
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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EP91102870A
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German (de)
English (en)
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EP0500979A1 (fr
Inventor
Christoph Maurer
Hans Matthiessen
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Draegerwerk AG and Co KGaA
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Draegerwerk AG and Co KGaA
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Priority to DE59107931T priority Critical patent/DE59107931D1/de
Publication of EP0500979A1 publication Critical patent/EP0500979A1/fr
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/403—Cells and electrode assemblies
    • G01N27/404—Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid, e.g. Clark-type oxygen sensors

Definitions

  • the invention relates to a measuring device for the detection of gases with the aid of an electrochemical sensor, the electrolyte chamber with its measuring electrodes being separated from the environment by a diffusion membrane, which is preceded by a diffusion barrier provided with at least one diffusion opening which can be changed in permeability.
  • GB-A-21 64 156 describes the construction of an electrochemical sensor with an electrolyte chamber, two measuring electrodes, a diffusion membrane, a counter electrode and a reference electrode.
  • the measurement-sensitive surface of the sensor is covered by an interchangeable cap, in which a plurality of passage openings are made, through which the gas to be detected passes to the diffusion membrane and becomes accessible for measurement.
  • the cap thus acts as a diffusion barrier, which must be replaced depending on the concentration of the gas to be detected, in order to prevent the sensor from being overloaded at elevated concentrations.
  • a number of diffusion barriers with a different amount of diffusion openings and / or different cross sections of the diffusion openings are available for this purpose. If the measuring range has to be changed because the amount of gas to be detected is either below or above the detection limit of the measuring range under consideration, the corresponding diffusion barriers must be replaced.
  • the lower limit of the measuring range corresponds to the detection limit
  • the upper limit of the measuring range is the respective Diffusion barriers used given by the amount of the detection gas transported, which can still pass through the diffusion openings. If this quantity transported exceeds the diffusion capacity of the diffusion barrier, the measuring device indicates that the measured value is too low. In addition, the characteristic curve - concentration versus measurement signal - then no longer behaves linearly.
  • the present invention has for its object to improve a measuring device of the type mentioned so that the sensor can be adjusted in its sensitivity to different measuring ranges during operation without external intervention and its response speed is faster.
  • the object of claim 1 is achieved in that the diffusion openings can be closed at the same time more or less with a valve device assigned to them, which is connected to a measured value comparator via a valve drive for changing the working position of the respective valve to be actuated before opening.
  • the object is achieved in that the single diffusion opening can be covered and continuously changed by an orifice arranged in front of it displaceably by the valve drive, the valve drive being connected to a comparator for changing the working position of the orifice.
  • the advantage of the invention can be seen in the fact that the measurement signal supplied by the sensor gives the comparator the necessary information so that it can decide whether the measurement range lies below or above a limit value range entered for it. If this limit value range is exceeded, the diffusion opening is enlarged accordingly in order to offer the increased supply of gas to be detected a larger opening of the diffusion barrier.
  • the changeability of the diffusion openings can either be done in stages by opening or closing individual or multiple valves, or there is only a single diffusion opening, which is, however, kept large enough and which can be continuously reduced or enlarged and even closed by means of a sliding diaphragm .
  • the detection sensor is based on a different measurement characteristic.
  • the automatic switching of the valve device makes it possible, depending on the required measuring range, to switch to the associated sensor characteristic curve and to operate the sensor automatically on the characteristic curve suitable for the measuring range.
  • the valve device controlled by the measured value via the comparator, makes it possible, depending on the required measuring range, to switch to the associated sensor characteristic curve and to operate the sensor automatically on the characteristic curve suitable for the measuring range.
  • there is a selectable family of characteristic curves and in the case of the single diffusion opening which can be continuously changed by an orifice, there is to a certain extent a characteristic curve continuum in which the sensor can be operated. This provides a fast measuring device with a wide range of applications, which reacts automatically to changes in the concentration of the measuring gas.
  • the comparator is equipped with a setpoint generator, which is connected in a feedback circuit to the valve drive, the change in the diffusion openings is controlled in such a way that this setpoint is always maintained by the sensor. If the concentration value of the gas to be detected therefore drops, which would result in the measured value falling below the desired value, the openings are enlarged until the sensor supplies a measured value corresponding to the desired value. If this does not take place even when the diffusion barrier is fully open, this state can be displayed by a corresponding display unit. If, in the other case, the concentration of the gas to be detected rises so high that the setpoint is exceeded, a corresponding number of diffusion openings are closed or the orifice continues to advance through the single diffusion opening until the sensor measurement signal matches the setpoint.
  • Such an arrangement makes it possible for even small deviations from the setpoint to be compensated for by a corresponding countermeasure which affects the size of the diffusion openings in the diffusion barrier, so that either the corresponding number of open or closed valves or that of the orifice plate distance traveled to open or close the single opening as a measure of the prevailing concentration of gas to be detected.
  • a sensor wired in this way responds very quickly to changing concentration values, although in terms of its electrochemical properties it can be quite slow in comparison, until it would reach the associated saturation measurement. Because in order to obtain a measured value, it is no longer necessary to wait until the sensor reaches its saturation measured value, but rather the entire one Measuring device arrangement regulates directly back to the set measuring signal setpoint.
  • a particularly favorable application for such a circuit arrangement results from the fact that, in order to protect the sensor when it is switched on, the smallest diffusion opening is first released to test whether the gas to be detected is present at all. If it is present, the diffusion barrier is opened more or less in accordance with the measurement signal. If there is no gas or the measurement signal is below a display threshold, the maximum opening cross-section of the diffusion barrier can be exposed in order to quickly reduce the opening cross-section when measuring gas occurs so that the specified target value of the measurement signal is reached.
  • the openings of the diffusion barrier as valve seats of different cross-section, which can be closed by means of a valve disk which can be controlled separately from the valve drive.
  • a diffusion barrier is obtained, which can be arranged directly in front of the diffusion membrane while taking up as little dead space as possible.
  • Another expedient embodiment of the diffusion barrier consists in that either a single or also several individual diffusion openings can be covered by a displaceably arranged diaphragm. Depending on the change in the measurement signal, a more or less larger number of Diffusion openings covered by the aperture, or a single existing diffusion opening is more or less exposed in its cross section.
  • valve plate A particularly rapid control possibility of the valve plate is given in that they are designed as a closure element made of piezoceramic, to which an electric piezo drive is connected as a valve drive.
  • Diffusion openings designed in this way have the advantage that they can be designed as particularly small and, under certain circumstances, expediently microstructured ceramic parts and that the piezo drive can be actuated almost free of electrical power loss.
  • the small size of the piezo parts further reduces the dead space of the valves.
  • An electrochemical sensor (1) with a measuring electrode (2) and a counter electrode (3) in an electrolyte chamber (4) filled with an electrolyte has a diffusion membrane (5) on the surface facing the surroundings, which is covered with a diffusion barrier (6) .
  • the diffusion barrier (6) has a plurality of diffusion openings (7) which are designed as a valve crater, each of which is covered with a valve plate (8) assigned to them.
  • the diffusion openings (7) have different opening cross sections, to which the valve plates (8) are adapted.
  • the valve plates (8) are controlled by solenoid valve drives, not shown, and receive the control impulses from a valve drive (9).
  • the measuring signal of the sensor (1) is passed from its measuring electrode (2) and counter electrode (3) to a measuring amplifier (10) and processed into a measuring signal (U).
  • the signal output (U) is fed to a comparator (11) and compared with a limit value defined in the comparator (11). If this limit value is exceeded or undershot, the valve drive (9) is actuated via a control line (12) and the corresponding valve plate (8) is actuated to open or close the associated diffusion opening (7).
  • Several different limit values can be stored in the comparator, when they are exceeded the control of one or more valve plates (8) are opened or closed separately or in combination with others, so that the sensor (1) detects the concentration ratios in the environment for the gas to be detected can be adjusted.
  • the sensor has a different one Characteristic curve (K1, K2, K3) as shown in Figure 2.
  • the characteristic curve (K1) corresponds to the sensitivity of the sensor 1 when the smallest diffusion opening (7) is open, the other two being closed.
  • the characteristic curve (K2) corresponds to the sensitivity of the sensor (1) when the smallest and the middle diffusion openings (7) are open, and the characteristic curve (K3) when all three are open.
  • the comparison of the measurement signal (U) on the comparator (11) with an associated limit value determines which of the valves (7, 8) must be opened or closed in order to maintain the required measurement range.
  • the operating point of the sensor (1) changes accordingly from one characteristic curve to the other. High concentrations are thus measured along the characteristic curve (K1), low concentrations along the characteristic curve (K3).
  • the sensor (1) with its diffusion barrier (6) is integrated in a compensation circuit by connecting its measurement signal to the inverting input of an operational amplifier (13), at the non-inverting input of which a constant voltage signal representative of a minimum concentration C MIN to be maintained is shown.
  • the output of the operational amplifier (13) is connected to the valve drive (9) via a feedback line (14). If the signal from the sensor (1) at the inverting input of the operational amplifier (13) deviates from the predetermined minimum concentration value, the operational amplifier (13) outputs a control signal to the valve drive (9), which, depending on the sign of the control signal, opens the diffusion opening Diffusion barrier (6) reduced (with positive deviation) or enlarged (with negative deviation of the sensor signal from the minimum concentration value C MIN ).
  • a display unit (15) connected to the valve drive (9) indicates the degree of opening of the diffusion barrier (6) and its display can be viewed directly as a measure of the prevailing concentration of gas to be detected.
  • the sensor (1) is operated according to the characteristic curve (K2) according to FIG. 2 with an assumed concentration of gas to be detected.
  • the minimum concentration value C MIN effective at the operational amplifier (13) specifies an upper limit for the characteristic curve of the sensor (1) which is thick on the characteristic curve (K2) from the zero point of the coordinate system (C, U) to the limit C MIN .
  • any further increase in the sensor voltage (U) does not lead to a further increase in the concentration value along the characteristic curve (K2), but remains at C MIN .
  • the constant course of the characteristic curve (K4) is achieved in that the valve drive (9) influences the diffusion barrier (6) in such a way that the diffusion openings only allow as much gas to be detected as is necessary to maintain the minimum concentration value C MIN .
  • the diffusion barrier has only a single opening (16) in the housing of the sensor (1) that keeps the membrane (5) free.
  • the diffusion opening (16) coincides with the housing opening of the sensor (1).
  • a diaphragm (17) is provided as a diffusion valve, which is attached to the valve drive (9) is connected via a linear guide (18).
  • the position of the linear guide (18) is shown on the display unit (15) so that it gives a direct measure of the concentration of the gas to be detected.
  • the wiring of the sensor (1) according to FIG. 4 can either take place according to the diagram corresponding to FIG. 1 or according to FIG. 3 and is not repeated in FIG. 4.
  • the orifice (17) is pushed more or less far back and forth in both directions of the directional arrow (19) by the valve drive (9) .
  • the diffusion opening (16) is opened accordingly.
  • the diaphragm (17) lies sealingly on the edge of the housing of the sensor (1), and its edge (20) which sweeps over the membrane (5) is chamfered in order to achieve the highest possible sensitivity in the area of small opening cross sections of the diffusion opening (16) with respect to the linear movement of the linear guide (18) and the released diffusion opening (16) in the region of small opening cross sections.

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  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Molecular Biology (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
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  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)

Claims (5)

  1. Appareil de mesure pour la détection de gaz au moyen d'un capteur électrochimique, dont la chambre à électrolyte, avec ses électrodes de mesure, est séparée de l'atmosphère à l'aide d'une membrane de diffusion, en amont de laquelle est placée une barrière de diffusion pourvue d'une ouverture de diffusion dont on peut modifier la perméabilité, caractérisé en ce que sont prévues plusieurs ouvertures de diffusion (7) qui peuvent être plus ou moins fermées, simultanément, au moyen d'un dispositif formant soupape (8) qui leur est associé, qui sont reliées à un comparateur de valeurs de mesure (11), par l'intermédiaire d'une commande de soupape (9), pour modifier la position de travail de la soupape (7, 8) à actionner.
  2. Appareil de mesure selon la revendication 1, caractérisé en ce que le comparateur (11) comporte un indicateur de valeur de consigne (13), qui est relié à la commande de soupape (9) selon un montage à réaction (14).
  3. Appareil de mesure selon la revendication 1 ou 2, caractérisé en ce que les ouvertures sont conformées en sièges de soupape (7) de sections transversales différentes, dont chacun est susceptible d'être fermé, individuellement, au moyen d'une tête de soupape (8) pouvant être commandée séparément par la commande de soupape (9).
  4. Appareil de mesure selon la revendication 3, caractérisé en ce que les têtes de soupape sont conformées en élément de fermeture (8) en céramique piézoélectrique, auquel est raccordé une commande piézoélectrique (9) servant de commande de soupape.
  5. Appareil de mesure pour la détection de gaz au moyen d'un capteur électrochimique, dont la chambre à électrolyte, avec ses électrodes de mesure, est séparée de l'atmosphère à l'aide d'une membrane de diffusion, en amont de laquelle est placée une barrière de diffusion pourvue d'une ouverture de diffusion dont on peut modifier la perméabilité, caractérisé en ce que l'unique ouverture de diffusion (16) est susceptible d'être recouverte et d'être modifiée de façon continue par un cache (17) monté devant celle-ci et déplaçable par la commande de soupape (9), la commande de soupape étant raccordée à un comparateur pour modifier la position de travail du cache.
EP91102870A 1990-02-23 1991-02-27 Dispositif de détection de gaz avec un capteur électrochimique et une barrière de diffusion variable Expired - Lifetime EP0500979B1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
DE59107931T DE59107931D1 (de) 1991-02-27 1991-02-27 Messgerät zum Nachweis von Gasen mit einem elektrochemischen Sensor und variabler Diffusionssperre

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE4005761A DE4005761A1 (de) 1990-02-23 1990-02-23 Messgeraet zum nachweis von gasen mit einem elektrochemischen sensor und variabler diffusionssperre

Publications (2)

Publication Number Publication Date
EP0500979A1 EP0500979A1 (fr) 1992-09-02
EP0500979B1 true EP0500979B1 (fr) 1996-06-12

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EP91102870A Expired - Lifetime EP0500979B1 (fr) 1990-02-23 1991-02-27 Dispositif de détection de gaz avec un capteur électrochimique et une barrière de diffusion variable

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US (1) US5092980A (fr)
EP (1) EP0500979B1 (fr)
DE (1) DE4005761A1 (fr)

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DE4018597A1 (de) * 1990-06-09 1991-12-12 Draegerwerk Ag Messelektrode fuer eine elektrochemische gasmesszelle
US5741413A (en) * 1993-12-18 1998-04-21 Sem Corporation Gas sensors and method of using same
GB9325916D0 (en) * 1993-12-18 1994-02-23 Sem Corp Improvements in gas sensors
US5624641A (en) * 1994-05-16 1997-04-29 Sem Corporation Gas sensing assembly
DE59509994D1 (de) * 1994-06-03 2002-02-21 Metrohm Ag Herisau Vorrichtung für die Voltammetrie, Indikatorelektroden-Anordnung für eine solche Vorrichtung, insbesondere als Teil einer Bandkassette, und Reihenanalyse-Verfahren für die Voltammetrie
GB9625463D0 (en) * 1996-12-07 1997-01-22 Central Research Lab Ltd Gas sensors
ATE421685T1 (de) * 1999-10-29 2009-02-15 Radiometer Medical Aps Verfahren und vorrichtung zum nachweis einer gasblase in einer flüssigkeit
US7640783B2 (en) * 2005-05-24 2010-01-05 Honeywell International Inc. Self-calibrating gas detector and method
DE102006026044A1 (de) * 2006-06-01 2007-12-06 Hochschule Karlsruhe Vorrichtung zur Bestimmung stark schwankender Gehalte flüchtiger Stoffe in Flüssigkeiten
ES2329533B2 (es) * 2006-10-30 2010-07-14 Universidad De Vigo Escudo piezoelectrico para sensores utilizados en aplicaciones medioambientales.
US8033157B2 (en) 2007-10-01 2011-10-11 Baxter International Inc. Medical fluid air bubble detection apparatus and method
US20100252451A1 (en) * 2009-04-01 2010-10-07 Warburton P Richard Gas monitor
KR20150022929A (ko) * 2012-05-30 2015-03-04 베코 테크놀로지스 게엠베하 교차 민감도를 고려하여 가스에서 탄화수소 프랙션을 탐지하기 위한 측정 장치 및 방법
US10900928B2 (en) * 2016-01-28 2021-01-26 Alcotek, Inc. Gas sensor

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DE2625895C3 (de) * 1976-06-04 1979-03-22 Auergesellschaft Gmbh, 1000 Berlin Vorrichtung zur Probennahme eines Gases bei der Bestimmung der Konzentration eines Gases in einer Atmosphäre
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DE3921526A1 (de) * 1989-06-30 1991-01-10 Draegerwerk Ag Diffusionsbarriere mit temperaturfuehler fuer einen elektrochemischen gassensor

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Publication number Publication date
US5092980A (en) 1992-03-03
EP0500979A1 (fr) 1992-09-02
DE4005761A1 (de) 1991-08-29
DE4005761C2 (fr) 1992-12-24

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